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Learning Objective Questions (items marked *** are required objectives)

After completing Chapter 4, students should be able to:

4.1               ***What important changes in the brain take place during infancy?

4.2               How do babies’ reflexes and behavioral states change?

4.3               How do infants’ bodies change, and what is the typical pattern of motor skills development in the first 2 years?

4.4               ***What are the nutritional needs of infants?

4.5               How does malnutrition affect infants’ development?

4.6               What are infants health care and immunization needs?

4.7               ***What have researchers learned about sudden infant death syndrome?

4.8               ***How do infant mortality rates vary across groups?

4.9               How do infants’ visual abilities change across the first months of life?

4.10            How do infants’ senses of hearing, smell, taste, touch, and motion compare to those of older children and adults?

4.11            How do researchers study perceptual development?

4.12            How do depth perception and patterns of looking change over the first two years?

4.13            How do infants perceive human speech, recognize voices, and recognize sound patterns other than speech?

4.14            What is intermodal perception?

4.15            What arguments do nativists and empiricists offer in support of their theories of perceptual development?



Apart from prenatal development, infancy is the period during which the greatest degree of physical change occurs.  An infant’s brain is developing much faster than the rest of her body, a developmental pattern that accounts for the typical “top-heavy” appearance of toddlers.


The Brain and the Nervous System


4.1       ***What important changes in the brain take place during infancy?


At birth, the midbrain and the medulla are the most fully developed structures of the brain.  These two parts, both in the lower area of the skull and connected to the spinal cord, regulate vital functions such as heartbeat and respiration as well as attention, sleeping, waking, elimination, and movement of the head and neck—all tasks a newborn can perform at least moderately well.  The least developed part of the brain at birth is the cortex, the convoluted gray matter that wraps around the midbrain and is involved in perception, body movement, thinking, and language.


Synaptic Development

All these brain structures are composed of two basic types of cells, neurons and glial cells.  Virtually all of both types of cells are already present at birth.  The developmental process after birth primarily involves the creation of synapses, or connections between neurons.  Synapse development results from the growth of both dendrites and axons.  Synaptogenesis, the creation of synapses, occurs at a rapid rate in the cortex during the first two years after birth, resulting in a tripling of the overall weight of the brain during those years. 


Brain development is not entirely smooth and continuous.  An initial burst of synapse formation in the first year or so after birth is followed by a pruning of synapses in each area of the brain, as redundant pathways and connections are eliminated and the “wiring diagram” is cleaned up.


This cycle of synaptogenesis followed by pruning continues through the lifespan.  With each cycle, the brain becomes more efficient.  Consequently, a one-year-old actually has a denser set of dendrites and synapses than an adult does, but the network operates far less efficiently than that of an adult’s.  Because infants have more unused synapses than adults, they can bounce back from a host of insults to the brain (such as malnutrition or head injury) much more easily than an adult.  Neuroscientists use the term plasticity to refer to the brain’s ability to change in response to experience.


There are several important implications from the cyclical, synaptogenesis-pruning feature of neurological development.

§         Brain development follows the old dictum: Use it or love it.  A child growing up in a rich or intellectual challenging environment will retain a more complex network of synapses than one growing up with fewer forms of stimulation.

§         The brains of infants possess greater plasticity than those of older children and adults.  Paradoxically, though, the period of greatest plasticity is also the period in which the child may be most vulnerable to major deficits.  A really inadequate diet or a serious lack of stimulation in the early months may cause subtle but long-lasting effects on the child’s later cognitive progress.

§         The brain changes significantly throughout the entire human lifespan.  New information about the continuation of the pruning process throughout childhood and adolescence and into adulthood has forced developmental psychologists to change their ideas about the links between brain development and behavior.



Another crucial process in neuronal development is the creation of sheath, or coverings, around individual axons, which electrically insulate them from one another and improve the conductivity of the nerve.  These sheaths are made of a substance called myelin; the process of developing the sheath is called myelinization


The sequence of myelinization follows both cephalocaudal and proximodistal patterns.  For example, nerves serving muscle cells in the hands are myelinized earlier than those serving the feet.  Myelinization is most rapid during the first two years after birth, but it continues at a slower pace throughout childhood and adolescence.  Other structures take even longer to become myelinized.  For example, the reticular formation is responsible for keeping your attention on what you’re doing and for helping you sort out important and unimportant information.  Myelinization of the reticular formation begins in infancy, but continues in spurts across childhood and adolescence and is complete in the mid-20s. 


Reflexes and Behavioral States


4.2       How do babies’ reflexes and behavioral states change?


Changes in the brain result in predictable changes in babies’ reflexes, sensory capacities, and patterns of waking and sleeping.  Such changes, or the lack thereof, can be important indicators of nervous system health.



Neonates have many adaptive reflexes that help them survive.  Some, such as automatically sucking any object that enters the mouth, disappear in infancy or childhood.  Others protect us against harmful stimuli over the whole lifespan, such as withdrawal from a painful stimulus.  Weak or absent adaptive reflexes in neonates suggest that the brain is not functioning properly and that the baby requires additional assessment.


The purpose of primitive reflexes—so called because they are controlled by the more primitive parts of the brain (the medulla and midbrain)—is less clear.  For example, if you make a loud noise or startle a baby in some way, you’ll see her throw her arms outward and arch her back, a pattern that is part of the Moro or startle reflex.  Stroke the bottom of her feet, and she will splay out her toes and then curl them in, a reaction called the Babinski reflex.  By about six months of age, primitive reflexes disappear.  When such reflexes persist past about six months, there may be some kind of neurological problem.


Behavioral States

Researchers have described five different states of sleep and wakefulness in neonates, referred to as states of consciousness.  Most infants move through these states in the same sequence:  from deep sleep to lighter sleep to fussing and hunger and then to alert wakefulness.  After they are fed, they become drowsy and drop back into deep sleep.  The cycle repeats itself about every two hours.  Neonates sleep as much as 90 percent of the time.  By six or eight weeks of age, the total amount of sleep per day has dropped somewhat, and we see signs of day/night sleep rhythms, called circadian rhythms.  Babies this age begin to string two or three two-hour cycles together, at which point we say that the baby can “sleep through the night.”  By six months of age, babies are still sleeping over 14 hours per day, but the regularity and predictability of the baby’s sleep is even more noticeable.  Of course, babies vary a lot around these averages.


Infants have a whole repertoire of cry sounds, with different cries for pain, anger, or hunger.  The basic cry, which often signals hunger, is usually a rhythmical pattern.  An anger cry is typically louder and more intense, and the pain cry normally has a very abrupt onset—unlike the more basic kinds of cries, which usually begin with whimpering or moaning.


Cross-cultural studies suggest that crying increases in frequency over the first six weeks, and then tapers off.  Parents across a variety of cultures use very similar techniques to soothe crying infants.  Most babies stop crying when they are picked up, held, and talked or sung to.  Parents sometimes worry that picking up a crying baby will lead to even more crying.  Research suggests that prompt attention to a crying baby in the first three months actually leads to less crying later in infancy.


For the 15 to 20 percent of infants who develop colic, a pattern involving intense bouts of crying, totaling three or more hours a day, nothing seems to help.  Neither psychologists nor physicians know why colic begins, or why it stops without any intervention.  It is a difficult pattern to live with, but it goes away at about three or four months of age.


Growth, Motor Skills, and Developing Body Systems


4.3       How do infants’ bodies change, and what is the typical pattern of motor skills development in the first 2 years?


Half of all the growth in a person’s life is completed by age 2.  Additionally, there are many qualitative changes, such as those that involve motor skills, that also happen during this period.


Growth and Motor Skills

Babies grow ten to 12 inches and triple their body weight in the first year.  At about age two for girls and age two-and-a-half for boys, toddlers are half as tall as they will be as adults.  A person’s adult height can be reliably predicted by doubling his or her height at age two to two-and-a-half.  Two-year-olds have proportionately much larger heads than do adults—obviously needed to hold their nearly full-sized brains.


Children acquire an impressive array of motor skills in the first two years.  Gross motor skills include abilities such as crawling that enable the infant to get around in the environment,  Fine motor skills involve use of the hands.


Explaining Motor Skill Development

Throughout infancy, girls are ahead of boys in some aspects of physical maturity.  Female infants may have a slight advantage in the development of fine motor skills, such as self-feeding.  Boys are typically more physically active, and acquire gross motor skills faster than girls do.


Despite gender differences in the rate of physical development, the sequence of motor skills development is virtually the same for all children, even those with serious physical or mental handicaps.  Children with mental retardation move through the various motor milestones more slowly than normal children, but they follow the same sequence.  Such consistencies suggest that motor development is controlled by an inborn biological timetable.


Esther Thelen suggested that the inborn timetable for motor skill development interacts with other aspects of physical development.  Her dynamic systems theory states the notion that several factors interact to influence development, including inborn genetic factors and environmental variables such as the availability of adequate nutrition.


Research supports the notion that experience influences motor development.  Opportunities to practice motor skills seem to be particularly important for young children who have disorders such as cerebral palsy that impair motor functioning.  Consequently, developmentalists are fairly certain that severely restricting a baby’s movement slows down acquisition of motor skills, and many are beginning to accept the idea that a baby’s movement experiences in normal environments may also influence skill development.


Developing Body Systems

During infancy, bones change in size, number, and composition.  Changes in the number and density of bones in particular parts of the body are responsible for improvements in coordinated movement, such as the wrist.  The process of bone hardening, called ossification, occurs steadily beginning in the last weeks of prenatal development and continuing through puberty.  Bones in different parts of the body harden in a sequence that follows the typical proximodistal and cephalocaudal patterns.  Motor development depends on ossification to a large extent.


Muscle fibers are virtually all present at birth although they are initially small and watery and contain a fairly high proportion of fat.  Changes in muscle composition lead to increases in strength that enable one-year-olds to walk, run, climb, and so on.


The lungs grow rapidly and become more efficient during the first two years.  Improvements in lung efficiency, together with the increasing strength of heart muscles, provide the two-year-old with greater stamina, or ability to maintain activity, than that of the newborn.  By the end of infancy, children are capable of engaging in fairly long periods of sustained motor activity without rest.



Babies depend on the adults in their environments to help them stay healthy.  Specifically, they need the right foods in the right amounts, and they need regular medical care.




4.4       ***What are the nutritional needs of infants?


Breast-feeding is substantially superior nutritionally to bottle-feeding.  Breast milk provides important antibodies for the infant against many kinds of diseases, especially gastrointestinal and upper respiratory infections.  It also promotes the growth of the nerves and intestinal tract, contributes to more rapid weight and size gain, and possibly stimulates better immune system function over the long term.


There are some situations in which breast milk is not sufficient to meet babies’ nutritional needs, such as preterm babies whose intestinal tracts are not as mature as those of full-term infants.  In addition to the immunological benefits of breast milk, they need supplements of amino acids and fats that full-term infants can manufacture.


All babies cannot be breast-fed.  Drugs are often present in the breast milk of mothers who are substance abusers or who depend on medications to maintain their own health.  In such cases, babies who are fed high-quality infant formula, prepared according to manufacturer’s instructions and properly sterilized, usually thrive on it.


Up until four to six months, babies need only breast milk or formula accompanied by appropriate supplements.  There is no evidence to support the belief that solid foods encourage babies to sleep through the night.  In fact, early introduction of solid foods can actually interfere with nutrition until four to six months of age.




4.5       How does malnutrition affect infants; development?


Malnutrition in infancy can seriously impair an infant’s brain because the nervous system is the most rapidly developing body system during the first two years.

§         Macronutrient malnutrition results from a diet that contains too few calories.  It is the leading cause of death of children under the age of five.

§         When the calorie deficit is severe, a disease called marasmus results.  Infants with marasmus weigh less than 60 percent of the weight expected for their age, and many suffer permanent neurological damage from the disease.  Most also suffer from parasitic damage from the disease which makes it very difficult to treat marasmus by simply increasing an infant’s intake of calories.

§         Some infants’ diets contain almost enough calories, but not enough protein, which can lead to a disease called kwashikor.  It is common in countries where infants are weaned too early to low-protein foods.  Like marasmus, kwashikor can lead to a variety of health problems as well as permanent brain damage.

§         Most nutritional problems in industrialized societies involve micronutrient malnutrition.  It is a deficiency of certain vitamins and/or minerals, such as iron or calcium.  Such deficiencies, although more common among the poor, are found in children of all economic levels.  Iron-deficiency anemia may impede both social and language development.


Health Care and Immunizations


4.6       What are infants’ health care and immunization needs?


Infants need frequent medical check-ups.  While much of well baby care may seem routine, it is extremely important to babies’ development.  For example, during routine visits to the doctor’s office or health clinic, babies’ motor skills are usually assessed.  An infant whose motor development is less advanced than expected for his age may require additional screening for developmental problems such as mental retardation.


One of the most important features of well baby care is the opportunity it provides for the vaccination of the infant against a variety of diseases.  Although immunizations later in childhood provide good protection against these diseases, the evidence suggest that immunization is most effective when it begins in the first month after birth and continues across childhood and adolescence.


In the U.S., the average baby has seven respiratory illnesses in the first year of life.  Babies in day-care centers have about twice as many infections as those reared entirely at home.  In general, the more people a baby is exposed to, the more often she is likely to get sick.


Neuropsychologists have suggested that the timing of respiratory illnesses that can lead to ear infections is important.  Infants who have chronic ear infections are more likely to have learning disabilities, attention disorders, and language deficits during the school years than their peers.  The reason may be because ear infections temporarily impair hearing, thus compromising the development of brain areas that are essential for language learning.  As a result, most pediatricians emphasize the need for effective hygiene practices in day-care centers, such as the periodic disinfection of all toys, as well as prompt treatment of infants’ respiratory infections.


A full set of immunizations includes vaccination for the following:

§         Three of hepatitis vaccine

§         Four of diphtheria/tetanus/pertussis

§         Three of influenza vaccine

§         Three for polio

§         One for measles/rubella

§         One for varicella zoster virus

§         Vaccination against hepatitis A is also recommended in some cities


INFANT MORTALITY (pp. 104-107)

Researchers define infant mortality as death within the first year after birth.  The rate has been declining for the past several decades, but the United States continues to have a high infant mortality rate than other industrialized nations.  Almost two-thirds of these infant deaths occur in the first month after birth and are directly linked to either congenital anomalies or low birth weight.


Sudden Infant Death Syndrome


4.7       ***What have researchers learned about sudden infant death syndrome?


Sudden infant death syndrome (SIDS), in which an apparently healthy infant dies suddenly and unexpectedly, is the leading cause of death between one month and one year of age.  Physicians have not yet uncovered the basic cause of SIDS, but there are a few clues. 

§         It is more common in the winter when babies may be suffering from viral infections that cause breathing difficulties.

§         Babies with a history of apnea, brief periods when their breathing suddenly stops, are more likely to die from SIDS.

§         SIDS is more frequent among babies who sleep on their stomachs or sides, especially if the baby is sleeping on a soft or fluffy mattress, pillow, or comforter.

§         Another important contributor is smoking by the mother during pregnancy or by anyone in the home after the child’s birth.

§         Imaging studies of the brains of infants at high risk for SIDS suggest that myelinization progresses at a slower rate than in others who do not exhibit such factors.  Babies’ patterns of sleep reflect these neurological differences and also predict SIDS risk.  Infants who show increasingly lengthy sleep periods during the early months are at lower risk of dying from SIDS that babies whose sleep periods do not get much longer as they get older.  Likewise, autopsies of SIDS babies have revealed that their brains often show signs of delayed myelinization.


Group Differences in Infant Mortality


4.8       ***How do infant mortality rates vary across groups?


Infant mortality rates, including deaths attributable to both congenital abnormalities and to SIDS, vary widely across racial groups in the United States.

§         Asian-American babies: about 5 per 1,000

§         Hispanic babies (Mexican American, Cuban American, and South and Central American): 5.6 per 1,000

§         White babies: about 5.9 per 1,000

§         Native-American babies: about 9.1 per 1,000

§         Native-Hawaiian babies: about 9 per 1,000

§         African-American babies: about 13.9 per 1,000

One reason for these differences is that infants in the higher-risk groups are two to three times more likely to suffer from congenital abnormalities and low birth weight—the two leading causes of infant deaths in the first months after birth—than babies in other groups.  Also, SIDS is two to three times as common in these groups.


Babies born into poor families are more likely to die than those born into families that are better off economically.  The statistics listed above suggest that the link between poverty and infant mortality is complex.


Mortality rates among babies of immigrants of all groups are lower than those of U.S.-born infants.  These findings challenge the poverty explanation for group differences in infant mortality because immigrant women are more likely to be poor and less likely to receive prenatal care than are women born the in the United States.  Many researchers suggest that lower rates of tobacco and alcohol use among women born outside the U.S. may be an important factor.


Access to prenatal care is another factor that distinguishes ethnic groups in the U.S.  The links among poverty, ethnicity, and infant mortality may be partly explained by access to prenatal care.


SENSORY SKILLS (pp. 107-109)



4.9       How do infants’ visual abilities change across the first months of life?


Visual acuity is the ability to see details from various distances.  It is fairly poor in newborns compared to that of adults, but it improves rapidly during the first year as a result of synaptogenesis, pruning, and myelinization in the neurons that serve the eyes and the brain’s vision processing centers.  Most children reach the level of 20/20 vision by about two years of age.  It is difficult to determine an infant’s true visual acuity because children can’t be tested with conventional eye exams until they are old enough to respond verbally to the examiner, typically at four to five years of age.


Infants can and do see and discriminate among various colors.  Infants’ ability to sense color, even in the earliest weeks of life, is almost identical to that of adults.


The process of following a moving object with your eyes is called tracking, and you do it every day in a variety of situations.  Because a newborn can’t yet move independently, a lot of her experiences with objects are with things that move toward her or away from her.  If she is to have any success in recognizing objects, she has to be able to keep her eyes on t hem as they move—she has to be able to track.  Infants younger than two months show some tracking for brief periods if the target is moving very slowly, but somewhere around six to ten weeks a shift occurs, and babies’ tracking becomes skillful rather quickly.


Hearing and Other Senses


4.10     How do infants’ senses of hearing, smell, taste, touch, and motion compare to those of older children and adults?



Although children’s hearing improves up to adolescence, newborns’ auditory acuity is actually better than their visual acuity.  Within the general range of pitch and loudness of the human voice, newborns hear nearly as well as adults do.  Only with high-pitched sounds is their auditory skills less than that of an adult.


Another basic auditory skills that exists at birth but improves with age is the ability to determine the location of a sound.  Newborns can judge at least the general direction from which a sound has come because they will turn their heads in roughly the right direction toward the sound.  Finer-grained location of sounds, however, is not well developed at birth, but by 18 months, it is nearly at the level seen in adults.


Smelling and Tasting

Smelling and tasting are intricately related.  Taste is detected by the taste buds on the tongue, which register four basic tastes: sweet, sour, bitter, and salty.  Newborns appear to respond differently to all four of the basic flavors


Senses of Touch and Motion

The infant’s senses of touch and motion may well be the best developed of all.  Reflexes, such as rooting and sucking, rely on the sense of touch.  Babies appear to be especially sensitive to touches on the mouth, the face, the hands, the soles of the feet, and the abdomen.  They are less sensitive in other parts of the body.



Perceptual skills focus on what the individual does with the sensory information—how it is interpreted or combined.


Studying Perceptual Development


4.11     How do researchers study perceptual development?


Researchers uses three basic methods that allow us to “ask” a baby about what he experiences.

§         In the preference technique, the baby is simply shown two pictures or two objects, and the researcher keeps track of how long the baby looks at each one.

§         Habituation is the process of getting used to a stimulus.  Its opposite is dishabituation, learning to respond to a familiar stimulus as if it is new.  Researchers present the baby with a particular sight or sound over and over until she habituates (she stops looking at it or showing interest in it).  Then experimenters present another sight or sound or objects that is slightly different for the original one and watch to see if the baby shows renewed interest (dishabituation).  If so, you know that she perceives the slightly changed sight or sound as “different” in some way from the original.

§         The principles of operant conditioning are the third option.  An infant may be trained to turn her head when she hears a particular sound.  After the learned response is well established, the experimenter can vary the sound in some systematic way to see whether or not the baby still turns her head.




4.12     How do depth perception and patterns of looking change over the first two years?


Developmentalists believe that infants’ patterns of looking at objects tell us a great deal about what they are trying to gain from visual information.


Depth Perception

One of the perceptual skills that has been most studied is depth perception.  It is possible to judge depth using any (or all) of three different kinds of information.

§         Binocular cues involve both eyes, each of which receives a slightly different visual image of an object.  The closer the object is, the more different these two views.  Information from the muscles of the eyes also tells you something about how far away an object may be.

§         Pictorial information, sometimes called monocular cues, requires input from only one eye.  When one object is partially in front of another one, you know that the partially hidden object is further away—a cue called interposition.  The relative size of two similar objects may also indicate that the smaller-appearing one is further away.  Linear perspective (like railroad lines that seem to get closer together as they are further away) is another monocular cue.

§         Kinetic cues come from either your own motion or the motion of some object.  If you move your head, objects near you seem to move more than objects further away, a phenomenon called motion parallax.   If you see some object moving, closer objects appear to move over larger distances in a space of time.

Infants seem to use kinetic information first, perhaps by about three months of age.  Binocular cures are used beginning at about four months.  Linear perspective and pictorial cues are used last, perhaps art five to seven months.


What Babies Look At

In the first two months, a baby’s visual attention is a search for meaningful patterns.  Babies scan the world around them until they come to a sharp light/dark contrast, which typically signals the edge of some object.  Having found an edge, the baby stops searching and moves his eyes back and forth across and around the edge.  Motion also captures a baby’s attention at this age.  Between 2 and 3 months, babies shift their attention from where an object is to what an object is.  As a result, they spend more time looking for patterns.


There is little indication that faces are uniquely interesting patterns to infants.  Babies do not systematically choose to look at faces rather than at other complex patterns.  Babies clearly attractive faces, and they prefer the mother’s face from the earliest hours after birth.




4.13     How do infants perceive human speech, recognize voices, and recognize sound patterns other than speech?


One of the central questions has to do with how early a baby can make discriminations among different speech sounds.

§         As early as one month, babies can discriminate between speech sounds like pa and ba.

§         By six months, babies can discriminate between two-syllable “words” like bada and baga and can even respond to a syllable that is hidden inside a string of other syllables, like tibati or kobabko.

§         It doesn’t seem to matter what voice quality the sound is said in.  By two or three months of age, babies respond to individual sounds as the same whether they are spoken by male of female or by a child’s voice.

§         Infants can rapidly learn to discriminate between words and non-words in artificial languages.


Babies are better at discriminating some kinds of speech sounds than adults are.  Up to six months of age, babies can accurately discriminate all sound contrasts that appear in any language, including sounds they do not hear in the language spoken to them.  At about six months of age, they begin to lose the ability to distinguish pairs of vowels that do not occur in the language they are hearing.  By age one, the ability to discriminate non-heard consonant contrasts begins to fade.


Newborns seem to be able to discriminate between individual voices.  They can tell the mother’s voice from another female voice, but not the father’s voice from another male voice.  The prefer the mother’s voice.  Premature infants are less likely to recognize their mother’s voices than babies born at term, suggesting that in utero learning may be responsible for newborn’s preference for the maternal voice.


Combining Information from Several Senses


4.14     What is intermodal perception?


Psychologists are interested in knowing how early an infant can integrate information from several senses, such as which mouth movements go with which sounds, a skill called intermodal perception.  Research suggests that it is not completely inborn.  Finding show that intermodal perception is possible as early as 1 month and becomes common by 6 months.  Intermodal perception is important in infant learning.  In older infants, intermodal perception can be readily demonstrated, no only between touch and sight, but between other modalities, such as sound and sight.


Explaining Perceptual Development


4.15     What arguments do nativists and empiricists offer in support of their theories of perceptual development?


The study of perceptual development has been significant because it has been a key battleground for the dispute about nature versus nurture.  Nativists claim that most perceptual abilities are inborn, while empiricists argue that these skills are learned.


There are strong arguments for a nativist position on perceptual development.  Research have found that more and more skills already present in newborns or very young infants.

§         Good auditory acuity

§         Poor but adequate visual acuity

§         Excellent tactual and taste perception

§         At least some color vision

§         At least rudimentary ability to locate the source of sound around them.

§         Capability of making quite sophisticated discriminations from the earliest days of life, including being able to identify their mother by sight, smell, or sound


Research with other species provides support for empiricism because that some minimum level of experience is necessary to support the development of the perceptual systems.


Studies of babies living in orphanages in Iran found that infants who didn’t have a chance to look at things, to explore objects with hands and eyes and tongue, and who were deprived of the opportunity to move around freely were retarded in the development of perceptual skills.


We can best understand the development of perceptual skills by thinking of it as the result of an interaction between inborn and experiential factors.  A child is able to make visual discrimination between people or among objects within the first few days or weeks after birth.  The specific discriminations she learn and the number of separate objects she learns to recognize, however, depend on her experience.  Both sides are correct—both nature and nurture are involved.